1. Field
The presently disclosed embodiment relates to a position detecting device using a reflection type photosensor, and particularly to a device for detecting a position and a moving distance of a moving target in an apparatus such as a camera.
2. Brief Description of Related Developments
Various actuators have been used for driving a lens, for example, in a digital still camera, a camcorder, a monitoring camera and the like, and in order to conduct sensing of a position of such a movable lens, etc., a position detecting device is used.
For example, there are, as a device for detecting a position and a moving distance of a focus lens, a device of a type using a pulse generator like a stepping motor system and a device of a type using a photosensor or a magnetic sensor for analogically detecting a moving distance in a piezo motor system. Examples of the former type are described in JP 04-9712 A, and examples of the latter type are described in JP 05-45179 A, JP 2002-357762 A, JP 2006-173306 A, JP 2009-38321 A.
The above-mentioned stepping motor system undergoes rotation for each of rotation angles corresponding to the number of counted pulses generated, and this stepping motor system is usually used for applications requiring long distance position detection. However, since a motor is not rotated continuously, noise during the rotation is large, which leads to generation of an acoustic noise when taking a moving picture image, and moreover, there is a defect such as a delayed response.
For that reason, in a digital still camera, etc., piezo motor systems which are suitable for preventing generation of an acoustic noise when taking a moving picture image, increasing a speed of autofocus and down-sizing of an apparatus are used increasingly instead of the stepping motor system.
FIGS. 4A and 4B show a position detecting device with a reflection type photosensor which can be used for position detection using a piezo motor system. As shown in FIG. 4A, a reflection type photosensor 1 is configured such that a light emitting element 3 is disposed on one concave portion partitioned with a light-shielding wall 2 and a light receiving element 4 is disposed on another concave portion. Also, as shown in FIG. 4B, a reflector 5 is provided at the side of a light-emitting/light-receiving surface SL of the photosensor 1 so as to be in parallel with the light-emitting/light-receiving surface SL and move in a direction where the light emitting element 3 and the light receiving element 4 are arranged in a line. According to the configuration as mentioned above, light from the light emitting element 3 is reflected on the reflector 5 and is inputted into the light receiving element 4, and the position and the moving distance of the reflector 5 (a moving target to which the reflector is attached) are detected by the amount of received light.
In the position detection using such a reflection type photosensor, an example of a technique for improving performance of position detection and moving distance detection is described in JP 2006-173306 A, and an example of improvement in linearity of an output signal is described in JP 2009-38321 A.
Meanwhile, in a digital still camera of high-power or high-end models, a single lens reflex camera, a camcorder, a monitoring camera and the like, for lens position detection of a camera module in which zoom function and long distance detection are necessary, there is a case where long distance detection of not less than 10 mm with high resolution of not more than 5 μm is required, and actually such detection has been difficult in conventional position sensing using a reflection type photosensor.
On the other hand, magnetic sensors are used in position detection of a piezo motor type being designed to prevent an acoustic noise when taking a moving picture image, to achieve high speed autofocus and to down-size an apparatus using a position detecting device. An example of such a magnetic sensor is shown in JP 2006-292396 A. In this magnetic sensor of JP 2006-292396 A, a magnetic field generating member (magnet), in which S-poles and N-poles are arranged alternately, and two magnetic field detecting elements (MR element or hall element) are provided, and the position detection is carried out by amplifying outputs of the magnetic field detecting elements and conducting arithmetic processing thereof.
However, in the use of the above-mentioned magnetic sensor, there are the following problems.
1) A system itself becomes a large size.
2) A system cost becomes high since a magnetic field generating member, in which many S-poles and N-poles are arranged, is used.
3) It is difficult to improve linearity of a signal due to a configuration for detecting strength of a magnetic field.
4) In the case where another magnet is used in a device provided with a magnetic sensor or the like, there is a possibility of causing malfunction of the device due to an influence of interaction between the magnetic fields and the like.
5) Since outputs from the two magnetic field detecting elements are low, they need to be amplified using an operational amplifier, which leads to high cost of components constituting the system.
6) An error of a magnetic force in magnetizing of S-poles and N-poles of a magnetic field generating member easily occurs, an intensity of a magnetic field is hardly kept constant, and performance is deteriorated due to oxidation of a magnet.
In order to solve the problems mentioned above, the applicant of the instant application proposed a position detecting device using a reflection type photosensor (JP 2013-36972 A). The position detecting device using a reflection type photosensor proposed by the applicant of the instant application is shown in FIG. 5. The reflection type photosensor 1 is configured such that a light emitting element (LED) 3 is disposed on one concave portion 6a and a light receiving element (phototransistor) 4 is disposed on another concave portion 6b and the both portions are separated by an outer peripheral wall and a light-shielding wall 2. A reflector 5 is arranged at the side of a light-emitting/light-receiving surface of the reflection type photosensor 1 so as to move in a direction (a direction shown by an arrow) being parallel to the light-emitting/light-receiving surface and being approximately vertical to an arranging direction (longitudinal direction in the figure) of the light emitting element 3 and the light receiving element 4. This reflector 5 is mounted on a moving target such as a lens so as to move together with it. On the reflector 5, reflecting portions “sa” and non-reflecting portions “sb” in the form of extra fine stripes are formed and arranged alternately (in the form of vertical stripes).
As shown in FIG. 5, three light receiving portions 4a, 4b and 4c, into which respective receiving regions are divided to be different light receiving regions in the moving direction of the moving target, are formed on the light receiving element 4 of the reflection type photosensor 1. Regarding three output signals (referred to as A, B and C, respectively) from these three light receiving portions, sizes and arrangement of the reflection type photosensor 1, the light receiving element 4 and the reflector 5 are adjusted so that the signal (output B) phase-shifting forward at 90 degrees to the reference signal (output A) and the signal (output C) further phase-shifting forward at 90 degrees can be obtained.
These outputs from the light receiving portions are inputted to the buffer amplifiers 7a, 7b and 7c, respectively, and then are inputted to an operation means (MPU) 8 where a neutral potential of these outputs is calculated from the output A and the output C, between which there is a phase difference of 180 degrees, and calculation of linear values are carried out to obtain the values having linearity. In the operation means 8, a neutral potential D=(A+C)/2 is calculated from the output A and the output C, between which there is a phase difference of 180 degrees, and (A−B)/(A+B) (=b) and (A+B)/(A−B) (=a) are calculated from the output A and the output B, between which there is a phase difference of 90 degrees.
According to this calculation of linear values, as shown in FIG. 6, by the calculation of the neutral potential D, the neutral potential of the outputs A and B is always set at 0 V, and therefore, the calculation result shows repeated triangular waveforms having high linearity. In FIG. 6, the outputs A and B converted into the values within a range of from −1 to +1 are shown. The results of the calculations are those obtained using the converted values. In the triangular waveforms of FIG. 6, portions falling to the right are obtained by the above-mentioned equation (A+B)/(A−B) (=a), and portions rising to the right are obtained by the above-mentioned equation (A−B)/(A+B) (=b).
In another example of calculation of linear values, a moving distance can be detected by calculating arctan (A/B) to obtain a phase angle θ of the signal. FIGS. 7A and 7B show the configuration such that a moving distance of a movable target can be detected by determining arctan (A/B) by enabling one cycle of the output signal of the reflection type photosensor to be obtained when the movable target moves the sum of the width of the reflecting portion and the width of the non-reflecting portion of the reflector 5 comprising the reflecting portions “sa” and the non-reflecting portions “sb”.
Meanwhile, in the position detecting device using a reflection type photosensor proposed by the applicant of the instant application, in order to obtain signals having a phase difference of 90 degrees for the calculation of arctan (A/B), the light receiving portions need to be arranged, as shown in FIG. 8, so that there are a portion where the light receiving portions 4a and 4b are overlapping and a portion where the light receiving portions 4b and 4c are overlapping when viewing from the light emitting element 3 side. FIG. 9 is a cross-sectional view of the overlapping portion cut in a longitudinal direction in FIG. 8. In the case where there are overlapping portions, as shown in FIG. 9, the travelling distance (shown by a full line with an arrow head) of light reaching the light receiving portion 4a or 4c after emitted from the light emitting element 3 and reflected on the reflector is not the same as the travelling distance (shown by a dotted line with an arrow head) of light reaching the light receiving portion 4b after emitted from the light emitting element 3 and reflected on the reflector. As a result, as shown in FIG. 10, there was a problem that the output voltages at the respective light receiving portions vary. There is the same problem when in FIG. 8, the light receiving portion 4b is located at the side of the light emitting element 3.
If the calculation of arctan is carried out using signals having varied output voltages, it leads to a problem that the pitch of the triangular waveforms shown in FIG. 7 is not the same and the detection of the position of the moving target cannot be carried out accurately.
Further, as shown in FIG. 10, detected positions indicating peak values of outputs of the light receiving element differ from each other, and curvatures of characteristic curves largely vary. As a result, in an actual application, there is a case where the following problem occurs.
In an application such as a camera lens module, the reflector 5 and the reflection type photosensor 1 are fixed to a movable part or a fixed part of an actuator casing. In this fixing, it is ideal if the reflector 5 and the reflection type photosensor 1 are located opposite to each other and the surfaces thereof are in parallel with each other. However, there is a case where the reflector 5 is fitted inclined with respect to the reflection type photosensor 1 due to poor accuracy in fabrication of the casing, fitting of the movable part, fitting of the reflector or fitting of the reflection type photosensor or from the viewpoint of application.
For example, FIG. 11 shows a configuration where the reflector 5 is fitted inclined with respect to the reflection type photosensor 1. When the reflector 5 fitted so as to be inclined moves, there arises a problem that a difference between the travelling distances of light reaching the light receiving portions 4a and 4c after emitted from the light emitting element 3 and reflected on the reflector 5 and the travelling distance of light reaching the light receiving portion 4b after emitted from the light emitting element 3 and reflected on the reflector 5 becomes larger, and a position detection accuracy is lowered.